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Abstract

Podostemaceae is the largest family of strictly aquatic flowering plants, with approximately 51 genera and 270 species. Many of these species are of conservation concern due to their delicate habitat within tropical waterways that are often dammed and used for hydroelectric power. We analyzed plastid nucleotide sequence data (matK, ndhF, and rbcL) using maximum likelihood inference to clarify phylogenetic relationships within the family. Our combined data set included 99 taxa, representing 93 species within 43 of the currently defined genera. Our results indicate that Podostemum is not monophyletic; Podostemum flagelliforme is an early diverging member of Podostemoideae and not closely related to other species in that genus. Additionally, various species of Rhyncholacis are more closely related to Autana, Macarenia, and Wettsteiniola, signifying that Rhyncholacis also is not monophyletic. Another important result is that the genus Thelethylax, despite the addition of new molecular data (ndhF and rbcL added to previously collected matK), remains unresolved in its placement.